Nowadays, with the movement toward small and light-weight portable radio terminals such as portable telephones, an extending whip antenna is attached to those so that it can be contained in the telephone body to improve the portability of the portable telephone in carrying and it can be pulled out from the telephone body in communicating to improve the antenna characteristic.
FIGS. 12 show an example of such an antenna unit: FIG. 12(A) shows the state where an antenna is pulled out from a telephone body, and FIG. 12(B) shows the state where the antenna is contained in the telephone body.
In these Figs., a metal fitting 12 for attaching and detaching the antenna is provided at the upper portion of the box 11 of the portable telephone body and a print distributing board 13 on which circuits are mounted is provided in the box 11. The metal fitting 12 is electrically connected to a high frequency circuit (feeding circuit) 14 on the board 13 via a spring 15.
The antenna body is composed of a fixed antenna unit 20 and a slide antenna unit 30. The fixed antenna unit 20 has a helical antenna 21 and the lower end of the helical antenna 21 is electrically connected to an antenna junction metal fitting 23 through a base 22. Further, the antenna junction metal fitting 23 is screwed in the metal fitting 12.
The helical antenna 21 is covered with an antenna cover 25 having a cylindrical cup shape and formed by insulation material and the opening of this cover 25 is attached to the antenna junction metal fitting 23. Note that, an antenna fixing unit 26 is provided at the center position of the upper end of the antenna cover 25.
An antenna cover 33 is provided so as to freely slide on the wind axis of the helical antenna 21 through the hole of an antenna fixing unit 26 and the hole at the center of the antenna junction metal fitting 23.
Furthermore, at the top of the antenna cover 33, a knob 34 for inserting and pulling out the slide antenna unit 30 is formed in one body, and in the vicinity position of that, a fixing part 35 having larger diameter is formed so that the fixing part 35 is fixed at the center hole of the antenna fixing unit 26 when the antenna cover 33 is contained in the box 11 so as to connect the fixing part 35 and the antenna fixing unit 26. Also, a conductive stopper 41 is attached to the lower end of the antenna cover 33 so that the lower end of a monopole antenna 31 is electrically connected to this stopper 41.
Note that, in FIGS. 12(A) and 12(B), the portion where hatching is not added other than the print distributing board 13 represents that it is made of conductive material.
According to the above structure, the lower end of the helical antenna 21 is connected to the high frequency circuit 14 via a signal path of the base 22--antenna junction metal fitting 23--metal fitting 12--spring 15 to supply electric power by the high frequency circuit 14 so that the helical antenna 21 operates as a transmitting/receiving antenna.
However, as shown in FIG. 12(B), in the state where the slide antenna unit 30 is contained in the box 11, the monopole antenna 31 is located at the position where it is not connected to the high frequency circuit 14 and is not electromagnetically connected to the helical antenna 21; thus the antenna 31 becomes the state where it does not regard transmission and reception.
Accordingly, in this case, transmission and reception, more particularly, reception of call incoming in carrying is conducted only by the helical antenna 21.
On the contrary, as shown in FIG. 12(A), when the slide antenna unit 30 is pulled out from the box 11, the lower end of the monopole antenna 31 is connected to the high frequency circuit 14 through a signal path of the stopper 41--metal fitting 12--spring 15 so as to receive electric power.
Further, in this state, the monopole antenna 31 is positioned on the wind axis of the helical antenna 21 and the top (upper end) projects from the upper end portion of the helical antenna 21 toward the outside. Accordingly, the monopole antenna 31 and the helical antenna 21 operate jointly so that the characteristic as a transmitting/receiving antenna is improved; thus transmission and reception in communicating is performed securely.
In the aforementioned antenna unit, its operation frequency is basically determined according to the antenna length of the helical antenna 21 and the monopole antenna 31. And the antenna unit and the high frequency circuit 14 are matched with each other by providing a matching circuit comprised of a condenser and a coil in the high frequency circuit 14.
By the way, frequency bands used in portable telephones is roughly classified into the following two:
(1) 800 MHz band . . . which is used in all over the world. PA1 (2) 1.5 GHz band . . . which is used in Japan. PA1 1.8 GHz band . . . which is used in Europe or the like. PA1 1.9 GHz band . . . which is used in US or the like.
Therefore, to improve the usability, a portable telephone capable of using for both frequency bands of terms (1) and (2) is required.
However, these frequency bands of terms (1) and (2) are different twice or more from each other. Accordingly, in the case where a portable telephone is used for both frequency bands of terms (1) and (2), two pieces of antennas operating for each frequency band are required.
Although, providing two antennas in one portable telephone is disadvantageous in smallizing considering the small size and light-weighting of a portable telephone, and it is disliked in design. Also, it is inconvenience for a user in that the user must select an antenna in accordance with the frequency band the user would like to use and pull out the antenna in communicating.
Furthermore, for example, with respect to the frequency used in the PDC (personal digital cellular) (800 MHz), the receiving frequency Rx is 810-826 MHz and the transmitting frequency Tx is 940-956 MHz: it is narrow in the respective bands but the frequency interval of each other is extremely large; thus it is difficult to plan such an antenna being resonant with for these both bands by using a general whip antenna, helical antenna or the like.